1. Field of the Invention
The present invention relates to an image forming device and an image forming method, and particularly relates to an image forming device and image forming method that apply liquid and form an image.
2. Description of the Related Art
Technologies relating to drying of liquids (inks, processing liquids and the like) are important in inkjet printing. As a technology relating to drying, Japanese Patent Application Laid-Open (JP-A) No. 2004-203034 has disclosed a technology that improves glossiness of an image in fixing processing, by drying excess moisture included in an ink.
Temperature and humidity inside a device vary with the influence of external air in which the device is placed and with ink amounts and paper types. In the technology disclosed in JP-A No. 2004-203034, the passage of a certain amount of time, depending on certain environmental conditions, printing conditions and drying conditions, is required from the start of printing until the temperature and humidity inside the device stabilize. Therefore, in practical applications, it is necessary to perform preparatory driving until the temperature and humidity are stable, and anything printed in this period becomes waste paper. This effect is relatively minor when printing large quantities of the same printed matter, but if printing details and paper types change frequently, for example, as in on-demand printing or variable printing, printing will finish before the temperature and humidity within the device are stable, and control of a drying section is not practically possible.
Moreover, a moisture amount that should actually be dried varies with an original moisture absorption amount of the paper, which depends on the weather of the day, and image density (which is to say ink amounts and processing liquid amounts). In addition, ease of drying varies with the type of paper. Therefore, it is necessary to carry out print tests beforehand in order to determine optimum temperature and humidity conditions for particular print data and environmental conditions.
Furthermore, it is thought to be necessary to carry out temperature and humidity measurements in the vicinity of a drying section, but measurement errors are likely to be caused by the influence of a hot wind from the drying section, a high-temperature heater or the like. Thus, temperature and humidity conditions may not always be accurately acquired.
JP-A No. 2007-111873 has disclosed a technology that enables an improvement of print quality at an aqueous varnish drying apparatus of a printer, by reliably performing drying of a varnish coating surface at an optimum temperature.
In the technology disclosed in JP-A No. 2007-111873, a paper face temperature reaches a target value that determines paper face drying conditions, provided ink and varnish amounts and the paper type are consistently at constant conditions. Ordinarily however, these conditions are variously changeable between print jobs. Therefore, in practical applications, it is necessary to perform print tests beforehand in order to determine the optimum paper face temperature condition.
JP-A No. 2000-62282 discloses a technology in which an occupancy ratio of regions with high print density levels is calculated from image data and, depending on whether or not this proportion reaches criterion values, output of a drying section is adjusted stepwise.
In the technology disclosed in JP-A No. 2000-62282, when a paper type or environmental conditions such as temperature and humidity or the like change, drying conditions change even if the image density is the same. Therefore, in order to determine the criterion values for setting the optimum output of the drying section for an image density, it is necessary to find conditions by test printing beforehand.
Against this technological background, if, for example, drying of a processing liquid is insufficient or subsequent ink coagulation is insufficient, failures in image formation occur, such as colorant floating because of a moisture layer at the paper surface and the like. If drying of an ink is insufficient, in a subsequent fixing process, image offsetting onto a fixing roller and/or a decrease in fixing strength (scraping or peeling) occur, and problems such as curl (warping) of the paper, cockling (ruffling) and the like arise.
On the other hand, if drying is excessive, problems such as cracking of images, damage to paper and the like occur, in addition to which electric power of the drying apparatus is wastefully consumed, which is inefficient. A drying apparatus accounts for a relatively large proportion of the power consumption of an inkjet printer. Therefore, inefficient drying leads to an increase in running costs.
With these conventional technologies, there has been a problem in that it is difficult to reliably dry liquids that are for forming images.